Recently, a system performing individual management, or a so-called RFID (Radio Frequency Identification) system, has been attracting attention in various industries. This RFID system is a technology that reads and/or writes data without making contact with the transponder by radio communications between a small non-contact integrated circuit (hereinafter referred to as “IC”) device that is called a transponder and a predetermined reader/writer. The transponder stores various readable and/or writable data and has a communication function. Various uses for this RFID system have been attempted such as in production/logistics by attaching a transponder as tags to goods, in transportation fare collection and identification cards, and electronic monies, for instance.
In such a RFID system, communication distance from several millimeters to several meters can be realized, and it is classified roughly from short communication distance: close contact type, proximity type, neighborhood type and distant type. Furthermore, carrier frequencies of 125 kHz, 134 kHz, 4.9 MHz, 13.56 MHz, 2.45 GHz, and 5.8 GHz are generally used in the RFID system. The carrier frequency of the short wave band 13.56 MHz has been standardized as ISO (International Organization For Standardization) 14443 and is becoming widespread.
Moreover, such a RFID system is classified roughly into two systems: an electromagnetic induction system and a radio wave system according to a data transmission method. The electromagnetic induction system transmits data on the magnetic flux produced from a reader/writer, and is mainly used for a short wave band under 13.56 MHz. This electromagnetic induction method has advantages such as it can be used under bad circumstances because it is less susceptible to rain or dust; it has a wide antenna directionality; it covers wide ranges of transmission; and it has an excellent permeability to non-conductive materials. On the other hand, the radio wave method transmits data on a radio wave generated from a reader/writer, and it is mainly used for high career frequencies. This electric wave method has advantages such as having a long communication distance compared with the electromagnetic induction method; having an antenna directivity; and it is easy to define the range of transmission.
The transponder operating in the electromagnetic induction method transmits and receives necessary voltage for operation and data by forming a parallel resonant circuit so as to convert magnetic energy to voltage efficiently (for example, see Japanese Patent Publication No. 3064840 and Japanese Patent Publication No. 3421334). Therefore, this kind of transponder often forms the resonant circuit with the loop antenna and the capacitor connected with the loop antenna in parallel so as to transmit and receive necessary voltage for operation and data. Basically, as shown in FIG. 14, the transponder has a circuit configuration in which an IC chip 103 is connected with a resonant circuit having an antenna coil 101 and a capacitor 102 disposed in parallel for tuning.
An internal type capacitor embedded in the IC chip 103 has been realized as the capacitor 102 to form the resonant circuit like this in addition to an external type capacitor connected to the IC chip 103 as shown in FIG. 14. Furthermore, a film capacitor type mounted on the antenna substrate has been suggested.
However, there are problems such as increasing the number of the parts and increasing manufacturing costs due to wages for connection to the IC chip when an external type capacitor is used as a capacitor to form a resonant circuit in a transponder operating in traditional electromagnetic induction methods.
Moreover, there is a problem that the manufacturing cost increases due to the area of the IC chip increasing when the internal type capacitor embedded in the IC chip is used as a capacitor having a resonant circuit in conventional transponders.
Furthermore, manufacturing costs increase because a through hole needs to be made for connecting the front and rear sides of the substrate electronically because the double-sided board needs to be used as an antenna substrate when a film capacitor type is used as a capacitor having a resonant circuit in traditional transponders.